1. Field of the Invention
This invention relates to an error concealing method of concealing uncorrectable errors when reproducing in a digital signal recording and reproducing apparatus.
2. Description of the Prior Art
A digital signal recording and reproducing apparatus for converting a video signal into a digital signal for record and reproduction corrects errors generated during reproduction based on error correcting parity added during recording. The digital signal recording and reproducing apparatus uses an error correcting code. However, for example, in event that a large scar is formed on a tape or when special effects are to be carried out such as slow and high speed play, the reproducing error rate is substatially increased, resulting in errors which cannot be corrected during the error correcting code. In such cases, an error concealment is applied to a detected error.
Error concealment of a video signal is realized by a method of interpolating from adjacent data or substituting data of an immediately preceeding frame, or the like. Here, in the case of using a bit rate reduction encoding in block units such as orthogonal transformation and the like, one error may have an expensive influence on all blocks so that it becomes difficult to conceal the error by interpolating from an adjacent data, and the error concealment is effected by substituting data of the corresponding block of a preceeding frame. In addition, in the case of using such a variable length coding as to finish with a plurality of blocks as a coding method, a variable length code fails to be synchronized with a word due to error when decoding, which means that such one error may have an expensive influence on a plurality of blocks. As a result, after decoding of an encoded data, an erroneous block has to be concealed. This means that a large-scale memory of one page or more is required for the concealment after decoding of an encoded data.
On the contrary, in case of concealing under the bit rate reduction encoded condition, a memory capacity for the concealment use may be made small. However, the concealment is required to be performed so as to correctly decode a variable length code when a concealed data is to be decoded. Accordingly, it is difficult to conceal an erroneous data under the encoded condition.